The present invention relates to breakout cables used for indoor applications. In particular, the present invention relates to a high fiber count ribbon sub-unit breakout cable that may be used throughout commercial buildings and the like for fiber optical wiring.
When wiring buildings or other premises, many cables typically must be used to make the desired connections throughout various areas within the premises. To accomplish the wiring, generally a group of cables are brought into the premises and then individual cables are wired for use in the various areas. Such wiring involves stringing the cables through plenums and risers within the premises which can cause breakage or damage to the fibers within the cables because of the stress placed on the cable during the stringing.
Ribbon fiber cable is one type of optical fiber cable that is often used for wiring buildings or other premises. Ribbon fiber cable comprises one or more fiber ribbons, with each ribbon comprising a multiplicity of fibers typically embedded in a thin, flexible supporting medium. One advantage of ribbon cable is its efficient use of duct or conduit space. For a given (relatively high) fiber count, a ribbon cable can have a significantly smaller outside diameter than a stranded cable, and therefore greater fiber density, than an equal fiber count stranded cable.
U.S. Pat. No. 5,857,051 discloses a cable made up of an arrangement of optical fiber ribbon structures. Strength members are arranged above and below the fibers in each ribbon structure. A sheath is used to surround the ribbon structure and associated strength members. The sheaths about each ribbon structure create a somewhat bulky cable which is not ideal for many tight spaced applications or applications which require that the cable have a small bend radius.
The optical fiber breakout cable according to the invention is a new, unique, small diameter, more robust cable capable of better protecting the enclosed optical fibers. The breakout cable is composed of optical fiber ribbons which are optical fibers protectively encased in a side-by-side relation. Such ribbons are well known in the art and have several advantages including individual protection of the optical fibers, ease of handling and ease of identification of individual fibers. The use of ribbonized cable is especially important in wiring premises because of the need to have fiber optic connections in many different areas of the premises. Thus once a cable enters the premises, the individual ribbon cables contained within the cable may be broken out and wired to different internal locations within the premises.
The optical fiber breakout cable according to the invention comprises a central member about which several sub-unit ribbon cables are helically stranded using a planetary stranding method. Each sub-unit ribbon cable contains a plurality of optical fibers in side-by-side relation, surrounded by strength members and encased by a ribbon protective jacket. A protective outer cable jacket encases all of the jacket protected sub-unit ribbon cables stranded about the central member.
The cable of this invention can advantageously be used for indoor applications such as riser or plenum cable, and may also be used for local distribution network, including external plant applications such as distribution or buried service cable, Because of the flexibility and relatively small diameter of the cable, it is particularly well-suited for a variety of environments where a small bend radius is required.